Currently, some personal listening devices such as earbuds, earphones, and headphones include an active noise control (ANC), also referred to as acoustic noise cancellation, system that improves the listening experience for the user by cancelling the external or ambient (environmental) noises from being heard by the user. The ANC technique cancels the external or ambient sound by generating a control signal that causes the personal listening device to introduce an anti-noise, which is an additional, electronically controlled sound field designed to counteract or destructively interfere with the desired external or ambient sound.
In some ANC systems, a reference microphone included in the personal listening device (PLD) may be used to pick up the primary noise source and to generate a reference signal. In some ANC systems, an error microphone also coupled to the personal listening device (PLD) may be used to detect the unwanted noise being heard by the user and to generate an error signal that represents the residual noise that may still remain despite the ANC system being in operation. The error signal monitors the ANC system's performance. The reference signal and the error signal may then be used to control the adaptation of the filters in the ANC system.
However, personal listening devices that perform ANC often have issues performing the ANC in a stable manner. For instance, when using the personal listening device while walking, running, or being on a slightly rough bus ride, the sound field captured by the reference microphone and the error microphone may vary substantially from the unwanted ambient noise that is to be cancelled. As a result, the adaptive filters converge to a wrong solution and the anti-noise being generated in accordance with this incorrect solution may include audible artifacts that can be significant enough to cause the user to feel uncomfortable or even nauseous.